low pressure governing system
TRANSCRIPT
PRESENTATION ON
GOVERNING SYSTEM
PRESENTED BY:BALGOPAL RAJU
ASSISTANT MANAGER (E&I)PERSONAL NO. :08303/08789
OPERATION DEPARTMENTCAPTIVE POWER PLANT (CPP)
NATIONAL ALUMINIUM COMPANY LIMITED (NALCO)
WHAT IS GOVERNING SYSTEM ROLE OF GOVERNING SYSTEM METHODS OF GOVERNING TYPE OF GOVERNING SYSTEMS CHARACTERISTICS OF GOVERNING SYSTEM HIGH PRESSURE GOVERNING SYSTEM LOW PRESSURE BYPASS SYSTEM
WHAT IS GOVERNING SYSTEM ?
WHAT IS GOVERNING SYSTEM
IT IS A GROUP OF DEVICES PROVIDED IN STEAM TURBINE
SYSTEM WHICH WORK IN COHERENCE TO MAINTAIN THE
SPEED OF T-G SET CONSTANT.
THIS CAN ALSO BE DEFINED AS :
IT IS A GROUP OF DEVICES WHICH INITIATE THE CORRECTIVE
ACTION TO RECTIFY THE DEVIATION OCURRED DUE TO
VARIATION IN SET RELATION BETWEEN INPUT AND OUTPUT.
BLOCK DIAGRAM OF GOVERNING SYSTEM
ROLE OF GOVERNING SYSTEM
ROLE OF GOVERNING SYSTEM
MAINTAIN THE TURBINE SPEED REASONABLY CONSTANT AT ALL
LOADS IN ORDER TO MAINTAIN THE GRID FREQUENCY WHEN
TURBINE IS CONNECTED TO GRID .
PROVIDE VERY FAST CONTROLLING ACTION.
SUCCESSFULLY LIFT AND CLOSE THE CONTROL VALVES ON
WHICH VERY LARGE STATIC AND DYNAMIC FORCES ACT.
ROLE OF GOVERNING SYSTEM (contd.)
PROVIDE A LINEAR RELATIONSHIP BETWEEN VALVE LIFT V/S
LOAD.
TO BE VERY SENSITIVE TO SPEED CHANGES OF THE ORDER OF
0.06% OF RATED SPEED (ie 1.8 rpm).
TO BE FREE FROM HUNTING AND NOT TO HAVE INDUCED
OSCILATIONS. (FOR ENSURING GOOD STABILITY A FEEDBACK
SIGNAL IS PROVIDED AT EVERY STAGE OF SIGNAL AMPLIFICATION).
TYPES OF GOVERNING-I
Nozzle Governing
Throttle governing
Bypass Governing
Governing is effected by varying the amount of steam which is further
done by changing the positions of control valves.
Any Throttling of Steam will lead to losses . In
governing system along with the change of quantity of steam the
quality of the steam also changes. Therefore Throttling should be
minimum.
NOZZLE GOVERNING
IN NOZZLE CONTROLLED TURBINES, STEAM FLOW IS
CONTROLLED BY SEQUENTIAL OPENING OR CLOSING OF
CONTROL VALVES ALLOWING STEAM TO FLOW TO ASSOCIATED
NOZZLE GROUPS.
THROTTLE GOVERNING
IN THROTTLE CONTROLLED TURBINES, STEAM FLOW IS
CONTROLLED BY SIMULTANEOUS OPENING OR CLOSING
OF ALL CONTROL VALVES ALLOWING THE STEAM TO FLOW
TO THE GROUP OF NOZZLES LOCATED ON THE ENTIRE
PERIPHERY.
THROTTLE GOVERNING
NOZZLE GOVERNIMG
All the valves in a set open or close
simultaneously / together.
The Valves in a set opens or closes
consequentially or in a sequence.
It is a Full arc Admission Turbine. It is a Partial Arc admission turbine
except at full Load.
It is most suitable for full load or
based Load plants.
It is good for Low load or variable
load turbines.
No operational Problems. May have operational Problem at
partial Loads.
BYPASS GOVERNING
It is employed in small capacity turbines running on high pressure
conditions and with small blading dimensions.
Here the loading up to approx. 80% ( Economic loading ) is met by
normal control valves feeding the First stage. For higher loading , to
supply more steam which is not possible due to small blading
dimensions ( can lead to operational problems) the extra quantity of
the steam is fed to the intermediate section of turbine bypassing the
initial high pressure stages.
TYPES OF GOVERNING-II
Constant Pressure Mode: Here pressure upstream of control valves is
kept constant and change is made by changing the position of control
valves.
Variable Pressure mode : Here control valves are in full open position and
pressure upstream of control valves varies proportionately with the load
requirement.
Response of Constant pressure Mode is much faster than Variable
pressure mode, but Constant pressure leads to more losses.
TYPE OF GOVERNING SYSTEMS
TYPE OF GOVERNING SYSTEM
MECHANICAL
HYDRO-MECHANICAL
HYDRAULIC
ELECTRO-HYDRAULIC
HIGH PRESSURE GOVERNING
MECHANICAL
HERE THE SPEED TRANSMITTER IS MECHANICAL
CENTRIFUGAL TYPE SPEED GOVERNOR WHICH ACTUATES
CONTROL VALVES THROUGH MEHANICAL LINKAGES.
PURE MECHANICAL GOVERNING SYSTEM ARE NOT USED FOR
UTILITY TURBINES NOW A DAYS.
HYDRO-MECHANICAL
IN HYDRO MECHANICAL GOVERNING SYSTEM SPEED
TRANSMITTER IS MECHANICAL CENTRIFUGAL TYPE SPEED
GOVERNOR. IT IS CONNECTED TO A HYDRAULIC SYSTEM
EITHER HYDRAULICALLY OR MECHANICALLY.
IN THE HYDRAULIC SYSTEM, THE SIGNAL IS AMPLIFIED SO THAT
CONTROL VALVES SERVOMOTORS CAN BE ACTUATED.
HYDRAULIC
IN HYDRAULIC GOVERNING SYSTEM SPEED TRANSMITTER IS
CENTRIFUGAL PUMP WHOSE DISCH. PR. IS PROPORTIONAL TO
SQUARE OF SPEED. THE PR. OIL IS SENT TO HYDRAULIC
GOVERNOR WHICH GENERATES A HYD. SIGNAL PROPORTIONAL
TO VALVE OPENING /CLOSURE REQUIRED.
THE HYD. SIGNAL IS SUITABLY AMPLIFIED THROUGH A HYD.
AMPLIFIER BEFORE APPLYING IT TO CONTROL VALVES
SERVOMOTORS.
HYDRAULIC GOVERNING IN STEAM TURBINES
HYD. AMPLIFIERwith F.U. Piston
HPCV SERVOMOTOR IPCV SERVOMOTOR
HPCV IPCV
HYD. SPEED GOVERNOR
HYD. SPEED TRANSMITTER
HYD. PRESS.
HYD. SIGNAL(ERROR)
HP SECONDARY OIL IP SECONDARY OIL
MECHANICAL COUPLING MECHANICAL COUPLING
ELECTRO-HYDRAULIC
IN ELECTRO-HYDRAULIC GOVERNING SYSTEM, SPEED TRANSMITTER IS
ELECTRICAL SPEED MEASURING DEVICE WHICH SENDS AN
ELECTRICAL SIGNAL TO ELECTRONIC CONTROLLER. AN
ELECTROHYDRAULIC CONVERTER CONNECTS THE CONTROLLER TO A
HYDRAULIC SYSTEM. THE HYD. SIGNAL IS AMPLIFIED SO THAT
CONTROL VALVES SERVOMOTORS CAN BE ACTUATED.
THE ELECTRO-HYDRAULIC GOVERNING OFFERS MULTIPLE
ADVANTAGES OVER OTHER THREE TYPES OF GOVERNING SYSTEMS
AND IS VERY POPULAR FOR UNIT RATINGS LARGER THAN 200 MW.
ELECTRO-HYDRAULIC GOVERNING IN STEAM TURBINES
EHCwith F.U.Piston
HPCV SERVOMOTOR IPCV SERVOMOTOR
HPCV IPCV
ELEC. SPEED TRANSMITTER
HP SEC. OIL IP SEC OIL
MECHANICAL COUPLING MECHANICAL COUPLING
ELECTRONIC CONTROLLER
ELECTRICAL SIGNAL
ELECTRICAL SIGNAL(ERROR)
COMPARISON – LOW vs HIGH PRESSURE
Characteristic Low pr.Gov. High pr. Gov.
Operating pr. 8/32 bar 160 bar
Size of actuator Bulky Small & compact
Command toActuator Hydraulic Electronic
No. Of pipe connection In Actuator 6 2
Gov. & ProtectionElements Hydraulic Electronic
Cf piping layout
Voluminous &Congested
Simple & compact
CHARACTERISTICS OF
GOVERNING SYSTEM
STEADY STATE SPEED REGULATION
Steady state speed regulation (also called proportional band, speed
droop etc.) Is defined as the ratio of % speed droop from no load to
full load to the nominal speed.
In the steam turbines equipped with electro- hydraulic governing
system, the speed regulation can be adjusted between 2.5 to 8% in
very fine steps.
TRANSIENT SPEED RISE
In the event of full load rejection, speed of the t-g set shoots up
temporarily before settling down to steady state value.
This temporary speed increase is called transient speed rise and is
expressed as percentage of rated speed.
Value of transient speed rise is restricted to 8% of rated speed.
DEAD BAND
Due to inherent inertia of the components of governing elements and
friction present in governing system, certain motion of governing
system is lost before corrective signal can actuate control valves. The
lost motion is called dead band of the system and is expressed as
percentage of the rated speed.
The order of dead band in Siemens turbines is 0.06%.
BLOCK DIAGRAM FOR LOW PRESSURE GOVERNING SYSTEM
S.No Name of Oil Source & pressure Purpose Colour Code
1. Control Oil MOP/AOP ( 7-8.5 Kg/cm2) To establish Trip Oil, Aux Trip Oil, Trip Oil, Start-up Oil, Aux Start-up Oil, Aux Secondary Oil, Secondary
Oil, Primary Oil, Etc2.
Trip OilMain Trip Valve (4.8-6
Kg/cm2)To reset , Open & Trip stop valve
3.Aux Trip Oil
Main Trip Valve (4.8-6 Kg/cm2)
To trip Hydraulic Trip Device
4.Start-up Oil
Starting Device ( 5.5 Kg/cm2)To assist Resetting & Opening Stop Valves
5. Aux Start-up Oil
Starting Device ( 5.5 Kg/cm2) To Reset Main Trip Valve & Hydraulic Trip Device
6. Aux Secondary Oil
Speeder Gear ( 2.3-4.8 Kg/cm2)
Input Signal to Hydraulic Converter
7. Secondary Oil (HP/IP)
Hyd/Electro-Hyd Converter ( 0-6 Kg/cm2)
To govern HP/IP Control Valve opening
8.Primary Oil
Primary Oil Pump ( 0-2.3 Kg/cm2)
Feedback speed signal for HG
9.Test Oil
Over Speed Test Device ( 2.0 Kg/cm2)
To test Over Speed Test Device
10. Drains
Diff. oils, their color codes, sources & purpose in KWU Governing System
CONTROL OIL OIL TAKEN FROM AOP/MOP DISCHARGE HEADER FOR THE GOVERNING SYSTEM
TRIP/AUX TRIP OILTHESE TWO OIL CIRCUITS ARE ESTABLISHED THROUGH MAIN TRIP VALVES UNDER RESET CONDITION.
START-UP/AUX START-UP OIL THESE TWO OIL CIRCUITS ARE ESTABLISHED TO ITS PEAK PRESSURE THROUGH STARTING DEVICE AT 0% POSITION AND PRESSURE STARTS REDUCING WHEN POSITION OF THE STARTING DEVICE IS RAISED.
AUX SECONDARY OIL THIS OIL CIRCUIT IS NOTHING BUT OUTPUT OF HYDRAULIC GOVERNOR AND INPUT TO HYDRAULIC CONVERTER.
SECONDARY OIL OUTPUT OF HYDRAULIC/ELECTRO-HYDRAULIC CONVERTER.
TEST OILTHIS OIL CIRCUIT IS ESTABLISHED TO TEST OVER SPEED TRIP DEVICE WHEN TURBINE IS RUNNING AT RATED SPEED.
REMOTE TRIP SOLENOID VALVESTHESE ARE TWO IN Nos. AND WHEN ANY TURBINE TRIP GETS INITIATED, THE SOLENOIDS GETS ENERGISED AND CONTROL OIL GETS DRAINED THROUGH THE VALVES AND TRIPS THE MTV.
MAIN TRIP VALVESTHESE ARE TWO IN Nos. AND CALLED THE MAIN TRIP GEAR. ALL THE TURBINE TRIPPINGS TAKE PLACE THROUGH THIS DEVICE. UNDER NON-TRIP CONDITION ESTABLISHES TRIP & AUX TRIP OIL AND USED FOR RESETTING/OPENING THE STOP VALVES AND PRODUCING HP/IP SECONDARY OIL.
STARTING DEVICE AS THE NAME OF THIS DEVICE SUGGESTS, THIS DEVICE IS USED FOR RESETTING AND OPENING THE STOP VALVES AND , MAIN TRIP VALVES & HYDRAULIC TRIP DEVICES. THIS DEVICE EITHER BE OPERATED MANUALLY BY HAND WHEEL OR FROM REMOTE (MCR) THROUGH MOTORISED ACTUATOR.
SPEEDER GEAR THIS DEVICE IN COMBINATION WITH STARTING DEVICE FORMS HYDRAULIC GOVERNOR AND PROVIDES INPUT HYDRALIC SIGNAL TO HYDRAULIC CONVERTER. THIS DEVICE EITHER BE OPERATED MANUALLY BY HAND WHEEL OR FROM REMOTE (MCR) THROUGH MOTORISED ACTUATOR.
HYDRAULIC/ELECTRO-HYDRAULIC-CONVERTERAMPLIFIES&CONVERTS HYDRAULIC /ELECTRICAL SIGNALS TO HYDRAULIC SIGNALS ( HP/IP SECONDARY OIL) FOR THE OPERATION OF HP/IP CONTROL VALVE.
HYDRAULIC TRIP DEVICESTHESE DEVICES PROVIDE MANDATORY PROTECTIONS OF THE TURBINE BY DRAINING AUX TRIP OIL. THESE DEVICES ARE RESET BY AUX START-UP OIL.
GOVERNING SYSTEM COMPONENTSGoverning Rack Consisting of following.
i) Emergency trip valve
ii) Tripping Device
iii) Change over valve
iv) Filters in control oil
v) Accumulator.
vi) Starting Device
vii) Hydraulic Amplifier with set of follow up pistons (HP&IP)
viii)Load shedding relay
ix) Trimming Device
x) Electro Hydraulic converter with set of follow up pistons (HP & IP)
xi) Extraction Relay
GOVERNING SYSTEM COMPONENTS
xii) Oil injection Test Device
xiii) Vacuum protection Device.
xiv)Set of solenoids for ATT operation.
HP Front Pedestal consisting of following. i) Impeller for primary oilii) Over speed trip governor HP Rear Pedestal Consisting of following. i) Thrust protection Device.ii) For brief description of above items, refer to O&M manualiii) HP and IP governing valves.
BOILER
Condenser
LP TURBINEIP TURBINEHP TURBINE
MS
MS
CRH NRV
HRH
HPSV
HPSV
IPSV
IPSV GENERATOR
HPCV
HPCV
IPCV
IPCV
CRH NRV
TG SET
AOP
MOP
AOP Discharge header
Filtered Control Oil
Remote Trip Solenoid Valves
Main Trip Valves
Hyd. Trip Device
TEST V/V STOP V/VSERVO MOTOR
STOP & CONTROL VALVE
CONTROL VALVE SERVO MOTOR
Hyd Converter
Electro-Hyd Converter
Starting Device
Secondary Oil
Trip
Oil
Aux Start-up Oil
Start-up Oil
Aux
Trip
Oil
Filtered Controlled Oil
Filter
BLOCK DIAGRAM OF GOVERNING SYSTEM
MAIN TRIP VALVE/TRIP GEAR• To open the trip oil circuit to drain, thereby closing all steam input to
turbine in case of abnormalities• At start up auxiliary start up oil keeps the MTV in uppermost position• Pressure oil enters and the outlet oil, Trip oil builds up and flows to
governing elements• The outlet oil through a hole fills auxiliary trip oil circuit.• The auxiliary trip oil keeps the MTV in upper position in normal condition.
(Aux. Start up oil will become ‘0’.• Any drop of aux. Trip oil pressure below certain limit will drop the MTV
and drains trip oil circuit.• Manually pressing the trip lever will also drain the trip oil circuit.• Limit switches provide electrical trip out signals
EMERGENCY TRIP SOLENOID VALVE
• It is installed in control oil line before main trip vales.• Remote operated from control room/protection circuit.• It has three connections pressure oil inlet, oil to MTV and drain• The two valve discs seals valve seats alternately• Solenoid not energized will make oil through to MTV• Solenoid energize will isolate pressure oil and drain the oil from
governing system
REMOTE TRIP SOLENOID OPERATED VALVES
TRIP OIL TO HOLD STOP V/V’S & AND TO PRODUCE SECONDARY OIL
AUX TRIP OIL TO HYDRAULIC TRIPING DEVICES
CONTROL OIL FROM AOP/MOP
AUX START-UP OIL TO RESET MTV & HTD
FilterDRAIN
AOP Dishargeheader
AOP/ MOP
RESETTING OF MTV
REMOTE TRIP SOLENOID OPERATED VALVES
TRIP OIL TO HOLD STOP V/V’S & AND TO PRODUCE SECONDARY OIL
AUX TRIP OIL TO HYDRAULIC TRIPING DEVICES
TRIPPING OF MTV THROUGH RTSV (ELECTRICAL)
CONTROL OIL FROM AOP/MOP
AUX START-UP OIL TO RESET MTV
FilterDRAIN
TRIPPING THROUGH RTSV
AUX TRIP OIL TO THE HYDRAULIC TRIPING DEVICES
AUX START-UP OIL TO RESET MTV
HYDRAULIC TRIP DEVICE
REMOTE TRIP SOLENOID OPERATED VALVES
TRIP OIL TO HOLD STOP V/V’S & AND TO PRODUCE SECONDARY OIL
AUX TRIP OIL TO HYDRAULIC TRIPING DEVICES
TRIPPING OF MTV THROUGH HYDRAULIC TRIP DEVICE (MECHANICAL)
CONTROL OIL FROM AOP/MOP
FilterDRAIN
AUX START-UP OIL TO RESET HYD TRIP DEVICES
TRIPPING THROUGH HYD TRIPDEVICE
STARTING DEVICE
AUX START-UP OIL TO RESET MTV
HYDRAULIC TRIP DEVICE
REMOTE TRIP SOLENOID OPERATED VALVES
TRIP OIL TO HOLD STOP V/V’S & AND TO PRODUCE SECONDARY OIL
AUX START-UP OIL TO RESET HYDRAULIC TRIP DEVICES
RESETTING OF RTSV, HYD. TRIP DEVICES & MTV
CONTROL OIL FROM AOP/MOP
FilterDRAIN
RESETTING OF RTSV, HYD. TRIP DEVICES & MTV THROUGH
AUX TRIP OIL TO THE HYDRAULIC TRIPING DEVICES
STARTING AND LOAD LIMITING DEVICE
• It can be operated either manually or by motor from control room.• At lower most position, it compresses bellow and ensures no secondary
oil generated.• At lowermost position, generates auxiliary start up oil and start up oil.• While raising up, aux, start up oil pressure first killed and subsequently
start up oil pressure reduced. This opens stop valves around 35%.• Further upward movement releases bellow and control valve starts
opening.• The release of bellow can be limited to limit the control valve opening,
thereby limiting the load.
TO TEST V/V OF STOP V/V
TO MTV & HTD V/V
CONTROL OIL FROM AOP/MOP
STARTING DEVICE
BRINGING THE STARTING DEVICE TO “0” POSITION TO BUILD START-UP & AUX STATR-UP OIL TO RESET STOP& MAIN TRIP VALVES AND HYD. TRIP
DEVICE
Aux Start-up Oil (5.5 Kg/cm2)
Start-up Oil (5.5 Kg/cm2)
RAISING STARTING DEVICE POSITION TO DE-PRESSURISE START-UP & AUX STATR-UP OIL TO OPEN STOP VALVES AND PRODUCING AUX SECONDARY
OIL
75 100
25
50
0
Starting Device
In %
Position at MCR
Drain
Drain
Hand Wheel
Motor
Start-up Oil (0 Kg/cm2)
Aux Start-up Oil (0 Kg/cm2)
STARTING DEVICE
STOP VALVE SERVOMOTOR
• Consists of two part piston. Disc shaped lower part connected to the valve stem. Other part is bell shaped. Two spiral springs are placed between the two halves.
Opening of valve• Trip oil is admitted to space above bell shaped piston and it is moved to
seat against the piston disc, forming single unit.• Then trip fluid admitted to space below piston disc and simultaneously
space above piston is drained gradually.• This causes the two haves moving towards open as single unit.• When trip oil pressure falls below certain value, the springs separate and
leads to closing of the valve.• Back seat of piston ensures minimum leakage of oil.• While closing, just before valve disc seats the oil draining is through
restricted area leading to braking action. Valve disc seats gently.
TEST VALVE FOR STOP VALVE• Function of test valve is to open and close stop valve manually or by start up
circuits/ATT.• Test valve forced downwards against spring either manually or by start up oil
pressure.• At bottom position of test valve, trip oil admitted above piston and below
piston connected to drain.• Test valve to be moved upwards either manually and by reducing the start up
oil pressure.• At top position of test valve, trip oil is admitted below piston and the above
piston is connected to drain.• Closing and opening of the stop valve can be checked by manually operating
the test valve. • HP and IP stop valves are opened in sequence at different pressures of start
up oil.
STOP VALVE SERVO-MOTOR
SPRING
CYLINDER
SPRING DISC
PISTON
PISTON DISC
TRIP OIL ABOVE PISTON
TRIP OIL BELOW PISTON DISC
RESETTING OPENING
TRIPPING
Drain
RESETTING/OPENING/TRIPPING OF STOP VALVE
RESETTING OF RTSV(DE-ENERGIZING) & HYD. TRIP DEVICES & MTV THROUGH STARTING DEVICE AT “0” POSITION
FilterDRAIN
STOP VALVE
OPENING OF STOP VALVES BY RAISING STARTING DEVICE
START-UP OIL TO TEST V/V
TRIP OIL TO STOP V/V
STOP VALVE SERVO-MOTOR
HYD TRIP DEVICE
DRAIN
AUX TRIP OIL TO HYD TRIP DEVICEAUX TRIP OIL TO HYD TRIP DEVICE
AUX START-UP OIL TO HYD TRIP DEVICE
AUX
STAR
T-U
P O
IL T
O
MTV
MTV
S/D
RTSV’S
TEST VALVE
STOP V/V OPERATION
FOLLOW UP PISTON• Follow up pistons converts the governor movement into oil pressure
changes.• Follow up piston consists of a hollow piston which can slide in acylindrical
body.• The position of piston is controlled by a tension spring and an adjusting
screw.• At lower end of piston a sleeve with two diametrically opposite drain ports
is sliding.• Similar ports in the piston overlaps with the sleeve ports in appropriate
position.• Below top cover of the body an inlet for trip oil through an orifice.• Oil supply after orifice is called secondary oil.
75 100
25
50
0
Starting Device
In %
75 100
25
50
0
Speeder Gear
In %
Starting Device Speeder GearPrimary Oil
Pump
Primary Oil (0-2.3Kg/cm
2)
Trip Oil From MTV
Aux Follow-up Valve
Link
Control Oil
Aux Secondary Oil To Hyd. Governor
Speeder Gear
Aux Follow-up Piston
Starting Device
HYDRAULIC GOVERNOR
Primary Oil
Trip oil From MTV
Aux Secondary Oil To Hyd. Governor Speeder Gear
Aux Follow-up Piston
Primary Oil Pump
Starting Device
Start-up oil
Aux Start-up oil
Control oil
75 100
25
50
0
Starting Device
In %
75 100
25
50
0
Starting Device
In %LINK
HYDRAULIC AMPLIFIER / CONVERTER
• It amplifies the signal from hydraulic speed governor.• The components are amplifier piston, pilot valve, follow up piston with
sleeve and mechanical feed back system.• Aux, sec oil flows over pilot valve. In steady state condition, pilot valve in
centre position. Pressure in aux. Sec oil is in equilibrium with spring force.• Pilot valve is kept in rotation for greater freedom of movement.• Deflection of pilot valve allows control oil above or below amplifier piston.• The motion of amplifier piston is transmitted via lever to the pilot valve as
feed back and pilot valve assumes centre position.• Each aux. Sec oil pressure corresponds to a certain position of amplifier
piston.
CONTROL VALVE SERVOMOTOR• The control valves operated by piston which is loaded one side with disc
springs and other side by hydraulic pressure.• Sec oil pressure controls the pilot valve.• During normal condition, CV at particular lift, pilot valve in equilibrium at
centre, balanced by sec oil pressure and spring force.• When sec oil pr. Raises the pilot lifts up and allows control fluid to below
piston to open the control valve.• The feed back cam mounted at the end of servomotor piston red returns
the pilot to its centre position by means of lever system and springs.• The pilot rotates continuously by means of control oil tangential jet from
disc and vibrates vertically by means of draining of sec oil at every revolution.
• Start of opening can be adjusted by adjusting pre-compression of spring with the adjusting screw provided at the fulcrum of the lever.
Secondary Oil
Drain
Drain
Drain ‘d’ Spring side
‘e’ Valve side
‘e’ Valve side
Control Oil
Pilot Valve of HPCVWhat happens when secondary oil pressure rises ?
What happens when secondary oil pressure decreases slowly ?
What happens when secondary oil pressure decreases very fast ?
CONTROL V/V SERVO-MOTOR
PROTECTIVE DEVICES IN
GOVERNING SYSTEM
1. Low vacuum trip device
2. Over speed trip device
3. Thrust bearing trip device
LOW VACUUM TRIP DEVICE• The function of the device is to trip the turbine on dropping of condenser
vacuum below a limit.• Condenser vacuum is connected to the top side of a diaphragm. The space
below diaphragm is at atmospheric pressure.• The control oil is admitted through aux pilot valve to the space below valve to
keep the valve in uppermost position against spring. The aux trip oil circuit is held blocked.
• As the vacuum deteriorates the diaphragm moves the pilot down and drains the control fluid causing the main valve to move down. The aux trip oil circuit is connected to drain causing turbine trip.
• Limit switches initiate alarm in control room.• Vacuum at which the device operates can be adjusted by the adjusting screw.• The device is isolated during start up. Aux pilot valve held upwards by spring
leading to develop aux trip oil pressure.• The primary oil pressure acting on the piston moves downwards in working
position of the device. This is to enable the protection after attaining certain speed.
Drain
Control Oil
Atmosphere
Vacuum
Aux Trip Oil
Drain
LOW VACUUM TRIP DEVICE
Resetting Of Low Vacuum Trip Device
Tripping Of Low Vacuum Trip Device
Low Vacuum Trip Device
OVERSPEED TRIP
• The function is to stop turbine when permissible speed is exceeded.• It is fitted in turbine rotor and consists of eccentric bolt, adjusting screw,
spring and screw plug.• By appropriate adjustment of screw, the centre of gravity of bolt is positioned
eccentrically to the turbine shaft.• Below the tripping speed the bolt is held in position by spring and bears
against the plug.• At speed higher than over speed limit, the centrifugal force overcomes the
spring force and forces the turbine rotor out of turbine. This activates the turbine trip mechanism.
OVER SPEED TRIP DEVICE
• The function of the device is to open the aux trip oil circuit to drain and shut down the turbine on over-speeding.
• The trip device situated in front bearing pedestal consists of valve body, pistons, pawls and spindle for limit switch operation.
• At over speed the eccentric bolt fly out of the shaft and strike the pawls and turning this against spring. The latches of the pawls release the piston and this piston moves towards shaft. The piston aided by aux trip oil pressure and spring loaded spindle.
• The aux trip oil pressure drops causing turbine trip.• Spindle provided with limit switches for alarm initiation.• For restarting the turbine the trip device is latched in by admitting the aux
start up oil.
OVER SPEED TRIP TEST DEVICE
• The function of the test device is to test the over speed trip device and trip bolt without actually raising the speed.
• Test device consists of three valves combined in valve block. One valve(left) is held at upper position by spring. In this position aux trip oil can pass to over speed trip device. When the knob is pressed, aux trip oil circuit to over speed trip device is blocked.
• The centre valve on moving downwards by rotating hand wheel admits test oil to the eccentric bolts causing them to protrude out of turbine shaft to strike against the pawl of trip device. The valve can be operated by motor during ATT.
• The third vale (right side) is used for resetting the over speed trip device after the test operation. When knob is pushed in against spring control oil enters aux start up oil circuit of over speed trip device and gets latched.
SEQUENCE OF OPERATION FOR TESTING OVERSPEED TEST DEVICE
1. Press the left valve knob to isolate the aux trip oil circuit to the over speed trip device.
2. Gradually rotate the hand wheel of middle valve to move downwards and observe for test oil pressure raise.
3. Observe and record the pressure at which the trip device is actuated. Raise pressure till both pins are acted.
4. Reduce the test oil pressure by moving the middle valve fully in opposite direction.
5. Press the right side valve knob to admit control oil to aux start up oil circuit of over speed trip device. This will reset the device to normal position.
6. Release the left side valve knob to normalize the aux trip oil circuit.
TURBINE OVERSPEED TRIP DEVICE
FLY BOTL
Aux Trip Oil
AUX START-UP OIL TO RESET
AUX TRIP OIL
Drain
TURBINE OVERSPEED TRIP DEVICE
THRUST BEARING TRIP DEVICE
• The function of the device is to drain the aux trip oil circuit in the event of high axial displacement of turbine shaft.
• The trip device consists of valve body, piston, pawl and limit switch.• During start up aux start up oil moves piston in latched position with pawl.• When shaft is axially displaced, the cam in the turbine shaft engages the pawl
to rotate. This moves the piston of trip device towards turbine shaft. The piston aided by aux trip oil pressure and spring force. The aux trip oil circuit is connected to drain causing turbine trip.
• Limit switch provided initiates alarm in the control room.• The healthiness of the trip device can be tested by admitting the test oil to the
piston to actuate the pawl.
TURBINE SHAFT
AUX START-UP OIL TO RESET
AUX TRIP OIL
DrainTRIPPING OF Thrust Bearing TRIP DEVICERESETTING OF Thrust Bearing TRIP DEVICETEST
OIL
THRUST BEARING TRIP DEVICE
a) Condenser vacuum is low ( > 0.6 bar absolute )
b) Spray water pressure is low (< 8.5 / 9.5 bar )
c) Temperature of condenser body is high (> 90° C )
PROTECTION DEVICES CAUSE CLOSURE OF BYPASS STATION IN CASE OF FOLLOWING EVENTUALITIES